150 



GEOLOGY OF THE E-ARRAGANSETT BASIK 



strike. Some of the larger masses, where weathered, show minute rounded 

 apertures, marking closely set pits. 



Under the microscope, in thin section, a specimen of the amorphous 

 limestone from this locality appeared as an aggregate of minute grains, 

 occasionally exhibiting large individual grains with distinct cleavage. 



Stratigraphically, the limestone is at this point relatively low down in 

 the red series of rocks. The material can be traced westward and north- 

 ward, by means of bowlders, in the same relative position on the east side 

 of the valley of Abbots Run. 



Eastward and northward, Kmestone is again found on the place of Mr. 

 Todd, near the old Powder House, in North Attleboro ; but here the hme- 

 stone is a mottled marble, which has been used for makhig quickhme. The 

 limestone bed here occurs in a thick section of sandstones and shales of red 

 color, in no way identifiable with the section in South Attleboro. This 

 occurrence is on a more northern line of outcrop than the former, and if 

 stratigraphically connected with it, is to be explained by a fold such as is 

 suggested by the general structure of this area. 



The irregularity of occurrence of the limestone in the different sections 

 where it is exposed, together with its evident secondary origin, has led to no 

 dependence being placed upon it in the course of the survey as a plane of 

 reference in the correlation of strata. 



Similar shaly hmestone reappears in the Norfolk County Basin, near 

 Canton Junction, Massachusetts, in a section described by me.^ A closely 

 similar rock occurs in the Cambrian section in North Attleboro, where the 

 limestone has evidently been formed from the remains of pteropods. 



These limestones were described by Prof Edward Hitchcock, and a speci- 

 men from the southwest part of Attleboro gave him the following analysis: ^ 



Analysis of limestone from AtllehorO} Massachusetts. 



CaGO$ 



SiOiamlAljOj 



Total ._. 



Quicklime 



Specific gravity, 2, 71. 



Per cent. 



94.60 

 5.40 



100. 00 

 52.98 



* Am. Jour, Sou, 3d series, Vol. XLVIII, 1894, p. 147. 



2 Final Eeport ou the Geology of Massachusetts, 1841, p. 80. 



